Sunday, April 27, 2014

A term in earth science: Great Oxidation Event

The atmosphere of today's Earth contains about 21% of oxygen (O2). Early in its history, the anoxic Hadean Earth—as it is scientifically proposed to have been existed around 4.4 billion years ago—had no interface of life-supporting oxygen. The Great Oxidation Event (GOE), which has been suggested to have occurred at the end of the Paleoproterozoic Era more than two billion years ago, was the time when some amount of free oxygen surfaced into the atmosphere. The appearance of the first atmospheric oxygen molecules was biologically and geologically induced. Then, photosynthetically produced oxygen paved the way for advancing forms of life and triggered the coevolution of the biosphere and the geosphere [1-3]. From the GOE onwards, Earth's atmosphere and oceans became oxygenated over time in stages [4].

The details of how atmospheric oxygen first rose to significant levels remain lost in geologic time. But ideas and answers are found by searching for fossiliferous formations such as ancient sandstone, black chert, black shale and stromatolites. Based on microbial mat fossils and fossil biomolecules, found in such deposits, researchers are looking for clues to understand the photobiochemistry of early organisms and possible routes of oxygen production. For example, fieldwork by Nora Noffke and others has turned up microbially induced sedimentary structures (MISS), including 3.48-billion-year-old MISS—the oldest ever reported [5].

An interesting aspect of this geobiological research is the interdependent, natural occurrence of organic and inorganic chemical processes throughout most of Earth's history. Robert M. Hazen and Dimitri Sverjensky argue that biodiversity and mineral diversity developed closely interlocked after oxygen became available within Earth's near surface environment [1]:
Our  recent chemical modeling suggests that the Great Oxidation Event paved the way for as many as three thousand minerals, all of them species previously unknown in our Solar System. Hundreds of new chemical compounds of uranium, nickel, copper, manganese, and mercury arose only after life learned its oxygen-producing trick. Many of the most beautiful crystal specimens in museums—blue-green copper minerals, purple cobalt species, yellow-orange uranium ores, and others—speak powerfully of a vibrant living world. These newly minted minerals are unlikely to form in an anoxic environment, so life appears to be responsible, directly or indirectly, for most of Earth's forty-five hundred known mineral species. Remarkably, some of these new minerals provided evolving life with new environmental niches and new sources of chemical energy, so life has continuously coevolved with the rocks and minerals.

Snapshots of the intertwined stories of our early home planet are now coming in view, thanks to groundbreaking discoveries. Will those results help us to understand and reconstruct the evolution of other planets and their moons in the solar system and beyond? Was the Great Oxidation Event a singularly Earth-bound affair?

Other terms for the Great Oxidation Event: Great Oxygenation Event, Oxygen Catastrophe, Oxygen Crisis, Oxygen Revolution and Great Oxidation.

Keywords: geophysics; planetary science; solar system; paleontology; mineralogy; paleochemistry; photosynthesis

References and more to explore
[1] Robert M. Hazen: The Story of Earth. The First 4.5 Billion Years, from Stardust to Living Planet. Penguin Books, New York, 2012; see page 180 and others.
[2] Robert M. Hazen: Mineral Evolution [hazen.gl.ciw.edu/research/mineral-evolution].
[3] Dimitri A. Sverjensky: Mineral Evolution [www.jhu.edu/~dsverje1].
[4] Heinrich D. Holland: The oxygenation of the atmosphere and oceans. Phil. Trans. R. Soc. B 2006, 361. DOI: 10.1098/rstb.2006.1838 [rstb.royalsocietypublishing.org/content/361/1470/903.full.pdf].
[5] Jim Raper: Geobiologist Noffke Reports Sign of Life that Are 3.48 Billion Years Old [www.odu.edu/about/odu-publications/insideodu/2013/11/11/topstory1].

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